Acoustic echo cancellers and their applications in the field of telecommunication are well known to those skilled in the art. Many such cancellers and related technologies have been described in various publications including the following patent documents:
U.S. Pat. No. 5,548,642 PA1 U.S. Pat. No. 5,530,724 PA1 U.S. Pat. No. 5,506,901 PA1 U.S. Pat. No. 5,428,562 PA1 U.S. Pat. No. 5,406,583 PA1 U.S. Pat. No. 5,394,392 PA1 U.S. Pat. No. 5,384,806 PA1 U.S. Pat. No. 5,329,586 PA1 U.S. Pat. No. 5,206,854 PA1 U.S. Pat. No. 5,163,044 PA1 U.S. Pat. No. 5,146,494 PA1 U.S. Pat. No. 5,016,271 PA1 U.S. Pat. No. 5,001,701 PA1 U.S. Pat. No. 4,918,685 PA1 U.S. Pat. No. 4,817,081 PA1 U.S. Pat. No. 4,464,545
A typical acoustic echo canceller currently available uses what-is-known-as an adaptive filter which employs a well-known algorithm such as the algorithm known as the Least-Mean-Square algorithm, or LMS. This algorithm continuously adapts to changes in the placement of both the speaker and microphone and to changes in loudspeaker volume. For these cancellers, a state machine is needed to automatically determine each of the four states, i.e., receiving, transmitting, double-talk, and idle. In addition, in order to cancel the echoes, these cancellers much be trained, that is, they must "learn" the loudspeaker-to-microphone acoustic response function for the room it is servicing. Also, the acoustic compensation length is determined by the length of the filter that is determined by the host resource availability.